Crystal controlled high-frequency oscillator



May 15, 1951 Filed May 29, 1950 1 BAND PASS FILTR 4 BAND PASS AllINVENTOR Jfin ATTORNEY duced.

Patented May 15, 1951 UNITED STATES PATENT OFFICE CRYSTAL CONTROLLEDHIGH-FREQUENCY OSCILLATOR company Application May 29, 1950, Serial No.164,961 In Great Britain June 15, 1949 The present invention relates tocrystal controlled high frequency oscillators incorporating a pluralityof crystals which may be selectively connected in the oscillator circuitfor determining the frequency of the electric oscillations pro- Hithertosuch switching has been effected by a conventional selector switch whichmust of necessity be at the same location as the oscillator.

The present invention has for an object to provide a switchingarrangement for selectively switching the crystals into the oscillatorcircuit which can be operated from a remote point. To this end,according to the invention, the crystals are each connected in theoscillator circuit through an individual rectifier, means being providedfor selectively biassing the rectifiers either to their conducting ornon-conducting state whereby the crystal to be connected in theoscillator circuit may be selected by the application of the appropriatebias to the corresponding rectifier. The application of the bias to thein dividual rectifiers may be easily effected from a remote point.

In one embodiment according to the invention, the oscillator is of thetype in which two valves are used and the crystals are connected betweentheir cathodes to provide feed back paths of low impedance at the seriesresonant frequency of the crystal. The crystals are permanentlyconnected in the circuit in series with individual rectifiers, which maybe of the thermionic or the barrier layer type. All the rectifiers mayhave one of their poles connected to the cathode of one of the valves ofthe oscillator, the other poles of the rectifiers being normallyconnected to a 5;

source of positive potential higher than cathode potential. Therectifiers are orientated so that normally they do not conduct by reasonof the more positive potentials applied totheir poles remote from thecathode. Switching means are provided, which may conveniently be locatedat a remote point for selectively reducing the potential applied to therectifiers whereby the rectifiers are selectively rendered conductingand thus connect the corresponding crystal in the oscillator circuit.

In a preferred form the positive bias for the rectifiers is derived fromthe high tension supply for the oscillator through one or moreresistances connected to a point intermediate 2. rectifier and itsassociated crystal. Each of these points is also connected to a contactof a selector switch whereby they may be selectively connected to earthor some other point of low potential. When one of these points isconnected to earth the bias- 11 Claims. (Cl. 250-.-36)

\ most satisfactory results.

sing potential on the corresponding rectifier is changed, by reason ofthe voltage drop through the resistances, and causes the rectifier toconduct and connect the associated crystal in the oscillator circuit.

In order that the invention may be clearly understood, reference willnow be made to the accompanying drawings in which a preferred embodimentof the invention is shown diagrammatically and by way of example.

In the drawings:

Fig. 1 is a circuit diagram of a known crystal controlled oscillator,and

Fig. 2 is a circuit diagram of a crystal controlled oscillator accordingto the invention.

Referring to Fig. 1 of the drawings, this shows a known form ofoscillator comprising two triodes I and 2, the output from valve i beingapplied to the grid 3 of valve 2 through any convenient known form ofband pass filter i. The positive lead from a source of supply of hightension current is indicated at 5. The cathodes 6 and l of the twovalves I and 2 are connected together through one of a plurality ofcrystals 8a, 8b, 80 by a selector switch 9. The crystals, which are ofdifferent resonant frequency, each provide a feed back path of lowimpedance at their series resonant frequency when connected in thecircuit by means of the selector switch. The valves are thus caused tooscillate at a frequency determined by the crystal selected.

With such an arrangement, the selector switch 9 must of necessity be atthe same location as the oscillator.

Referring now to Fig. 2 which shows an oscillator according to theinvention with remotely controlled switching, valves 1 and 2 are coupledtogether in a basically similar manner to those of Fig. l and similarparts are given the same reference numerals. In this arrangement,however, the crystals 8a, 8b, 8c are permanently connected between thecathodes 6 and i of the two valves by means of parallel leads Ill, ll,l2 connected to leads [3, l4, l5 respectively. Connected in the leads13, Hi, l5 are rectifiers I8, I! and I3 respectively. These may be ofany convenient type, such as diodes or barrier layer type, but germaniumdiodes have been found to give the the rectifier poles which are themore negative in the conducting state of the rectifiers, that is thecathodes in the case of diode rectifiers, are biassed to a positivepotential such that the rectifiers are rendered non-conducting. To thisend, leads l3, l4, I5 are connected through resistors I9, 20, 2! leads22, 23, 24 and resistors 25, 26, 21 respectively to a common lead 28connected to the positive high tension lead 5 and containing a commonresistor 29. Earthing condensers 30, 3|, 32 ar connected to the leads22, 23, 24 respectively. The last mentioned leads are also connected byleads 33, 34, 35 respectively to a remotely situated selector switch I09analogous to the switch 9 of Fig. 1 for selectively rendering operativethe crystals 8a, 8b, 80 by selectively connecting to earth, or to someother point of low potential, the positively biassed poles of therectifiers I6, I I, I8.

Each position of the switch I99 completesthe circuit between the cathode6 of valve I, and earth, through the corresponding rectifier I6, I! orI8 and the corresponding crystal 8a, B1), or 80 is thereby connectedinto circuit. The cathodes or equivalent poles of all the otherrectifiers are biassed positively by the resistor network and as theyhave a high resistance when so biassed, the

remaining crystals are isolated from the circuit.

The crystals 8a, 8b, 80, may be of any convenient kind, for examplequartz crystals and may operate at fundamental or overtone frequency.Preferably they are operated at or near fundamental frequency, higherfrequencies being obtained by additional frequency multiplying stages inknown manner.

Whilst a particular embodiment of the invention has been described, itwill be understood that various modifications may be made withoutdeparting from the spirit of the invention.

I claim:

1. In a crystal controlled high frequency oscillator, a plurality ofcrystals each operable to control the frequency of said oscillator, arectifier connected in series with each of said crystals, means forbiassing each of said rectifiers to a non-conducting state and means forselectively reducing said bias.

2. In a crystal controlled high frequency oscillator, a plurality ofcrystals each operable to control the frequency of said oscillator, arectifier connected in series with each of said crystals, means forbiassing each of said rectifiers to a non-conducting state and remotelysituated means for selectively reducing said bias.

3. In a crystal controlled high frequency oscillator, a plurality ofcrystals each operable to control the frequency of said oscillator, arectifier in series with each of said crystals, means for positivelybiassing each of said rectifiers to a nonconducting state and means forselectively conmeeting said rectifiers to a point at a lower potentialthan said biassing potential.

4. In a crystal controlled high frequency oscillator, a plurality ofcrystals each operable to control the frequency of said oscillator, arectifier in series with each of said crystals, means for positivelybiassing each of said rectifiers to a nonconducting state and a remotelysituated selector switch for selectively connecting said rectifiers to apoint at a lower potential than said biassing potential.

5. A crystal controlled high frequency oscillator comprising twothermionic valves, a plurality of electrical conducting paths betweenthe cathodes of said valves, a rectifier and a crystal connected inseries in each of said conducting paths, means for biassing each of saidrectifiers to a non-conducting state, and means for selectively reducingsaid bias.

6. A crystal controlled high frequency oscil latorcomprising twothermionic valves, a plurality of electrical conducting paths betweenthe cathodes of said valves, a rectifier and a crystal in series in eachof said conducting paths, means for positively biassing each of saidrectifiers to a non-conducting state, and a remotely situated selectorswitch for selectively connecting said rectifiers to a point at lowpotential.

7. In a crystal controlled high frequency oscillator, a plurality ofcrystals each operable to control the frequency of said oscillator, adiode in series with each of said crystals, means for positivelybiassing the cathode of each of said diodes to a non-conducting stateand means for selectively connecting said cathodes to a point at a lowerpotential than said biassing potential.

8. A crystal controlled high frequency oscillator comprising twothermionic valves, a plural-- ity of electrical conducting paths betweenthe cathodes of said valves, a diode and a crystal connected in seriesin each of said conducting paths, means for positively biassing thecathode of each of said diodes to a non-conducting state, and a remotelysituated selector switch for selectively connecting said diode cathodesto a point at low potential.

9. An oscillator as claimed in claim 8 wherein the diodes are germaniumdiodes.

10. An oscillator as claimed in claim 5 wherein the rectifiers are ofthe barrier layer type.

11. An oscillator as claimed in claim 5 wherein the oscillator operatesat approximately the fundamental series resonant frequency of thecrystals.

JOHN A. FRY.

No references cited.

